> publicizing how this works will come back to bite them in the butt

I didn't see any rules or heuristics published. Merely that they employ a multi-stage filter (as any engineer could imagine), and that they codify their ruleset with a human-readable DSL (which is kind of interesting, but also kind of weird).

  > The difference between a blog comment and a twitter post is negligible.

The difference in textual content between a tweet and blog comments falling within a similar character length are perhaps negligible, though there is often no such length constraint in place for blogs. Comment spam strategies are free to vary string length to optimize for evasion, click through, proliferation, and other criteria. I would also argue there is a different demographic distribution between Twitter and blogs with regard to readership and participation.

That said, Twitter just outlined a number of reasons why their case is special. They are a high-availability, high-volume, low-latency service. Twitter's spam solution was designed to handle their very special set of constraints. I think a multi-stage filter complete with asynchronous post-processing jobs would be a bit much for your average Wordpress blog. People just starting out with (say, PHP) probably can't fathom a multiprocess deployment architecture. Not to say they couldn't, but the journey is a long one.